Carbon based industrial chemical processes often give rise to aqueous effluent streams carrying a variety of carbon containing compounds. Thus, for example, it is known that the Synthol or Fischer-Tropsch Synthesis in which hydrocarbons, aliphatic alcohols, aldehydes and ketones are produced by the catalytic hydrogenations of carbon monoxide gives rise to an aqueous byproduct or effluent stream, known as the "Fischer Tropsch organic acid stream". This stream typically contains between 1% and 3% of C.sub.2 to C.sub.5 monocarboxylic acids along with non-acidic chemicals such as ketones and aldehydes. This stream is conventionally treated by an activated sludge to strip the stream of its carbon content before recycling the purified water into the cooling circuit of the plant or running it into a river or the sea. The resultant biomass is either incinerated or may be disposed of as fertilizer.
In an unrelated field of technology it is known that certain microorganisms, known as oleaginous organisms, are capable of producing edible oils which oils have become known as Single Cell Oils or SCO's. [See for example the overview SINGLE CELL OIL edited by R. S. Moreton, Longman Scientific & Technical, 1988]
According to the work of Moreton referred to above, the first truly commercial SCO process is the one being carried out at the plant of Sturge Biochemicals in the United Kingdom at which a lipid rich in gamma linolenic acid [GLA; 6,9,12-octadecatrienoic acid] is produced. According to a report by K. W. Sinden of John and E. Sturge Limited [Enzyme Microb. Technol., 1987 Vol. 9 p. 124-125] the microbial oil rich in GLA is produced by a Mucor sp. cultivated on a pure defined substrate based on glucose.
Gamma Linolenic Acid is a high value product which occurs in several natural products including breast milk, evening primrose oil, oats and other products. In the human and animal body it is converted to prostaglandin E.sub.1, one of the important localised hormone type products regulating the body functions of the kidneys, liver, lungs, brain, nerve system and immune system. Products containing GLA are presently widely used in many parts of the world as a component of health food programs.
A large number of oleaginous organisms has been reported in the literature. The feedstock range on which such oleaginous organisms may be cultivated to produce lipids is quite diverse. According to literature reports such feedstock ranges from molasses, bananas, whey and potato starch to exotic carbon sources such as pentose, hexose sugars, disaccharides, glycerol, amino acids and ethanol. In general all such organisms are capable of assimilating glucose and other sugars while some are capable of assimilating starches. Reports on microorganisms capable of being cultivated on simpler forms of carbon-containing chemicals such as ethanol and glycerol do exist but relate to only a small number of specific SCO producing organisms.
It has been reported in Japanese patent application 81012479 that the microorganisms Mucor javanicus, Rhizopus delemar and Aspergillus asumi mut. shirousamii may be cultivated on waste water discharged from brewing, starch, rice, confectionary and cake producing or food processing factories. It will be readily appreciated that such waste water contains starch and/or sugars which are known nutrients for sustaining the growth of those microorganisms.
It has further been reported in European Patent Application 0269351 in the name of Lion Corporation that certain gamma-linolenic acid producing microorganisms may be cultured with fatty acids or fatty acid esters, more particularly fatty acids of between 8 and 22 carbon atoms as carbon source for the production of gamma-linolenic acid.
In European Patent Application 0155420 it is reported that microorganisms of the Mortierella genus may be cultured on glucose to produce a lipid rich in gamma-linolenic acid and that the efficiency of the culture is enhanced by the addition of acetic acid or an alkali metal acetate.
From the aforegoing it will be seen that the search for alternative producers of lipids rich in gamma-linolenic acid and for alternative feedstocks for use as a carbon source for such organisms is ongoing as it would clearly be advantageous to provide a process by which lipids rich in gamma-linolenic acid may be produced from simpler forms of carbon source materials.
It has now been found that certain non-starch and non-sugar carbon containing compositions based on mono carboxylic acids having between 2 and 5 carbon atoms, and in particular acetic acid, are capable of being used as a feedstock for the cultivation of certain oleaginous microorganisms capable of producing valuable Single Cell Oils. This unpredictable finding is made even more surprising by the fact that the feedstock in question does not sustain the growth of all oleaginous microorganisms. Furthermore, such feedstock, according to presently available results, does not appear to sustain growth of the organisms in question throughout their entire life cycle. Although the organisms germinate from spores introduced into the feedstock and develop to the hyphal stage, the organisms do not generally proceed to the stage of sporulation with the result that the feedstock in question would not appear to be capable of constituting a natural ongoing habitat for the organisms capable of sustaining successive life cycles until the carbon source is depleted. Despite the incomplete life cycle we have found that the organisms in question are capable of converting the simple chemical compounds present in the feedstock in question into high value oils and other chemical products.
It has further been found that the Fischer-Tropsch organic acid stream, which contains C.sub.2 to C.sub.5 mono-carboxylic acids can be used as a feedstock carbon source for the cultivation of certain oleaginous microorganisms.